In 3G (UMTS) networks, an RNC (Radio Network Controller) is connected to multiple base stations (Node Bs). One of the RNC functions is to manage handover between Node Bs during mobility; i.e. where a handset moves from being attached to one Node B (the source) to another (the target).
In 4G/LTE, the eNodeBs are also physically connected via a common controller: the Serving Gateway (SGW), which also acts as a mobility anchor during handover. However, there is also a new interface: X2. This is generally a point-to-point interface between adjacent eNodeBs without need to go via the SGW. In summary, the usual route data takes is from the internet, via the SGW and source eNodeB to the terminal. During handover the source eNodeB creates a one-time tunnel to the target eNodeB using the X2 interface, and proxies the data traffic through that (bypassing the SGW). Once the handover is complete, the tunnel is removed and data travels via the SGW to the target eNodeB (the SGW to target eNodeB connection is being established in the background during handover).
Mobile Edge Computing involves processing power hosted at (or close to) the network edge, typically an eNodeB. This brings benefits of low latency, since application data does not need to traverse the Internet, and hence improves customer experience.
The Edge cloud utilises servers installed at the radio network ‘edge’, usually the eNodeBs. By having processing/storage/server hardware one (or two) hops away from the terminal, it is possible to reduce latency and internet backhaul costs, as well as realise hyper-localised services relevant to a given eNodeB.
A cloud deployment of these servers involves virtual machines (VMs) that encapsulate the server-side of a given application into its own runtime. These VMs are then managed by a central controller (‘Hypervisor’) responsible for starting/stopping/provisioning them. Multiple VMs can run on a single Edge server, therefore many applications can benefit from the low-latency of reduced backhaul.
In known systems the target eNodeB is unaware of any session data that the VM collected during its tenure on the source eNodeB. Therefore the advantage of Edge servers (low latency) is mitigated by not having the advantage of session persistence. Internet servers (in contrast to edge servers) can persist sessions (they do not care which eNodeB the terminal is attached to, and the application session will persist) but do not have the advantage of low latency.